In conventional two-wheel drive electric model vehicles, the vehicle is braked exclusively by the driven wheels. By short-circuiting its motor windings, the primary electric motor brakes the driven wheels through the drivetrain. The two driven wheels are usually the rear wheels in order to provide optimum driving traction when the vehicle accelerates forward.
However, braking a forward-moving vehicle with only the rear wheels causes increased forward weight transfer, a shifting of the vehicle's weight to the front tires. This forward weight transfer limits the maximum deceleration which braking the rear wheels can provide. If too much braking force is applied to the rear wheels, the vehicle's rear tires may begin to slide, causing a loss of control of the vehicle. Consequently, a conventional two-wheel drive electric model vehicle may only apply very little brake force if the driver is to maintain control of the vehicle.
Thus, the braking capabilities of conventional two-wheel drive electric model vehicles are limited. Because electric motor brakes are applied through the drivetrain, it is infeasible to simply add the braking system used for the drive wheels to the non-drive wheels. Such an addition would effectively introduce the same expense and other considerations as producing a four-wheel drive vehicle. It would be desirable if a braking system permitted the application of greater braking force without an accompanying loss of control.
Additionally, a conventional radio transmit controller only provides two channels of information to the model vehicle receiver: the position of the throttle trigger and the position of the steering wheel. The position of the throttle trigger controls three operations: forward acceleration, reverse acceleration, and braking. However, a conventional throttle trigger can be moved in only two directions: pulling the throttle trigger toward the user and pushing the throttle trigger away from the user.
Typically, the model vehicle's Electronic Speed Control (ESC) uses the speed and direction of the vehicle motor to determine if the throttle trigger controls forward and reverse acceleration, forward acceleration and braking, or reverse acceleration and braking. When the vehicle motor speed is at or below a speed threshold, the ESC permits the user to select between forward and reverse acceleration. Forward acceleration is performed by pulling the throttle trigger from a neutral position toward the user and reverse acceleration is performed by pushing the throttle trigger from the neutral position away from the user. When the motor is moving at above the speed threshold, the ESC permits the user to select between further acceleration in the same direction and braking. Further acceleration is performed by continuing to pull or push the throttle trigger, depending on which direction the vehicle motor is moving. Braking is performed by moving the throttle trigger to the opposite position, a position which would have caused acceleration in the other direction if the motor speed were at or below the speed threshold.
A disadvantage of this approach is that the trigger position used to brake varies depending on the direction the vehicle is currently accelerating. An alternative approach is a “one direction only” mode for the ESC. The one direction only mode may also be called a “forward only” mode when it permits acceleration in the forward direction, and may also be called a “reverse only mode” when it permits acceleration in the reverse direction.
When set to a one direction only mode, the ESC may consistently interpret all pulling on the throttle trigger from the neutral position as an instruction to accelerate the electric motor in a particular direction. The ESC may consistently interpret all pushing on the throttle trigger from the neutral position as an instruction to brake the electric motor. In both cases, the magnitude of the acceleration or braking force typically increases with the distance from the neutral position. A one direction only mode may permit consistent throttle positions to accelerate or brake the vehicle, but has the disadvantage of only permitting the vehicle to move in one direction.
It would be desirable if a transmit controller could permit the same positions of a throttle trigger to consistently accelerate and brake a model vehicle, regardless of the speed and direction of the vehicle motor, while still permitting both forward and reverse acceleration.
It would further be desirable if both the desired enhanced braking and transmit controller features described above could be implemented in an existing model vehicle, with a minimum of replacement of conventional vehicle components.